It is well-known that in the operation of internal combustion engines, fuel combustion results in the formation of substantial amounts of water and various acidic gases (e.g., CO.sub.2, SO.sub.x, NO.sub.x, HCl). Inevitably, a portion of this water and acidic material leaks past the rings and condenses in various internal areas of the engine, causing rusting. The problem is particularly critical when this rusting causes sticking and malfunction of closely fitting parts in hydraulic valve lifter systems and oil pump relief valves.
Traditionally, alleviation of rusting has been obtained by including an overbased sulfonate in the oil formation. Typically, the overbased sulfonate contains a metal carbonate which dissolves in the produced water and tends to neutralize the water-soluble acids. In addition, the sulfonate itself has some tendency to preferentially wet the ferrous engine surfaces and hence to displace adsorbed water droplets. Unfortunately, this protection is usually inadequate thereby often requiring the use of supplemental additives, such as alkyl phenolethylene oxide condensates. Even with the aid of supplemental additives, protection is often inadequate to prevent serious rusting of engines where operation is such as to condense much blowby or where periods between oil drains are long.
It is therefore apparent that a need exists for improved rust inhibitors which will alleviate the problems discussed in the foregoing.
I have found that certain acidic derivatives of benzene, while not soluble themselves in mineral oil, can be complexed into mineral oil by means of alkenyl succinimide dispersants. Under such conditions these acidic derivatives of benzene are effective as rust inhibitors. Still further, a synergism in rust inhibition is provided by a combination of the designated materials with overbased sulfonates.